Experimental Study on the in-plane behavior of standing seam roof assembly and its use in lateral bracing of rafters
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The standing seam roof (SSR) system is the most commonly used roof system for metal buildings due to its superior durability, water tightness, and energy efficiency. In this type of system, SSR panels attach to Z-shaped or C-shaped purlins with clips, and the purlins are in turn connected to rafters (i.e. roof beams). For the design of the rafters against lateral torsional buckling, bottom flange braces provide torsional bracing to the rafter and the SSR system provides some lateral bracing. However, the degree to which the SSR system can restrain the rafter against lateral movement has not previously been studied. The objective of this study is to quantify the in-plane strength and stiffness of the SSR system and identify how this can be used to provide lateral bracing to the rafter. A total of 11 full-scale standing seam roof specimens were tested to investigate the effects of different standing seam roof configurations (SSR panel type, clip type, thermal insulation, and purlin spacing) on the in-plane stiffness and strength of the SSR system. The resulting stiffness and peak strength of the specimens were tabulated and compared for different SSR configurations. Results showed that the in-plane load-deformation behavior of SSR systems was governed by clip deformations and that variations in the type of SSR panel or clip can have a major impact on the strength and stiffness of the specimens. A specimen with vertical rib panels was shown to have 16 times more stiffness than a similar specimen with trapezoidal rib panels because the vertical ribs restrain the clip deformation. However, even a small standoff was found to reduce the stiffness of vertical rib SSR assemblies with more than three-fold drop in stiffness as the standoff was increased from 0 in. to 0.4 in. Trapezoidal rib SSR assemblies had consistent strength stiffness with fixed clips having standoff of 0 in. or 0.5 in., but with floating clips the stiffness decreased with increasing standoff. Addition of blanket insulation and thermal blocks were found to result in 60% to 350% increase in stiffness. A method for using these experimental results in calculations of required bracing for metal building rafters is described. An example is also provided which demonstrates that the SSR roof can contribute to bracing of the rafter and may reduce spacing or size of discrete/point torsional braces.